For some years, there has been a great deal of interest in achieving more efficient utilization of electrical power generation capabilities and more sophisticated control of electrical loads by users. With a growing awareness of the ecological impact and economic cost of inefficient utilization of resources, electrical power consumers have become aware of the desirability of altering their usage patterns. Some power companies already offer rates which vary according to the time of day, to encourage customers to operate appliances such as clothes dryers, pool pumps and dishwashers during off-peak times. Generally, a high rate is charged during certain hours of peak demand and a lesser rate is charged during other hours of off-peak demand. An alternative approach would permit extension of time-of-day rate setting to allow more frequent (e.g., hourly) changes in rates. That would require, though, that the customer be advised of each rate change and then decide what appliances the customer is willing to operate at such rate. To automate this process, it is necessary that the power customer be able to monitor and control power usage by the more significant loads in the customer's residence or business.
However, the customer typically sees the benefits of time-managed appliance usage only when studying a monthly bill, which provides very little information. The customer does not really know, under real usage conditions, how much it costs to operate one appliance compared with another. To make these cost comparisons using monthly billing statements probably is not practical because it is not realistic to conduct a multi-month-long controlled experiment wherein all other energy consumption is constant except for the use of a first appliance one month and the use of a different, second appliance another month. Without such a controlled experiment, one cannot determine, from a monthly bill, the cost of operating a specific appliance or even the comparative cost of operating two different appliances, or how much will be saved by operating a given appliance at any specific rate. Accordingly, a need exists for a system which will provide to a customer, on a timely basis, reports on the amount of power consumed by one or more appliances and the cost of operating those appliances.
A need further exists for allowing a customer to make cost-based decisions as to the operation of appliances, and for effectuating those decisions. Many utility customers may wish to control their expenditure for electric power. For example, the customer might be willing to operate a swimming pool heater only so long as the energy cost is below an amount set (i.e., predetermined) by the customer, or only so long as the outside temperature is in a certain range. As yet another example, the decision to replace an aged, inefficient appliance may be deferred by a customer who does not know how quickly a new, more efficient appliance will pay for itself through reduced energy consumption because the consumption by the old, existing appliance is not known. Commercial customers may be enabled to make process selection decisions based on relative energy costs, if those costs can be demonstrated.
Since the rates charged for electric energy are at least in part a function of system-wide demand at the time (as, for example, reflected in fuel cost), a customer with a fixed budget can consume more power when rates are low than it can when rates are higher. Therefore, such a customer may wish to be able to make usage decisions which are rate-dependent. Of course, if rates can be changed by the utility company at any time, the customer is not likely to want to sit around listening to or watching broadcasts of rate information. An automatic response to rate broadcasts would be desirable. Such an automatic response could assume many forms and might be conditioned not only on the newly announced rate, but also on other factors, such as the sensed temperature or time of day or urgency of a task (e.g., appliance priority level). The inability to respond automatically may be one of the factors which has inhibited the development of flexible rate-change broadcasting, existing rate-change broadcasting being limited generally to signaling the beginning and end of peak and off-peak rate periods.
Allowing customers to control their usage patterns and implement usage decisions, though, only deals with one aspect of power management. Sometimes the voluntary. behavior of customers is not enough to avert problems such as excessive power demands. Ideally, a load management system would allow not only the user, but also the power supplier (i.e., utility company), to have at least some degree of control over the loads connected to the power mains.
These interests have lead to a variety of systems for allowing control functions such as "load shedding" (that is, selectively turning off devices, or loads) to be performed. For example, there are numerous home and building automation systems both available commercially and available in the literature. Many of these automation systems allow the user to schedule appliances to turn on, or to be operated, only at defined times. Some allow specially-equipped appliances to be rendered inactive during periods of declared higher rates or demand. Few, if any, though, allow the power supplier (in addition to the customer) also to remove loads from the system selectively (e.g., to target specific loads of specific customers) or allow them only to turn on at or during preset times.
In the event of a power outage, as may occur from a natural event, such as a storm, or the development of an excessive load, as may occur from an extreme weather situation (e.g., a heat wave or unusual freeze), a great problem is presented to electric utility companies. The instant power is restored or a large disconnected load is brought back on line, the energization of all the loads connected to the power distribution grid or the reconnected loads, as the case may be, causes a huge current surge which can induce a large transient voltage spike due to load, line and transformer inductances, and which can destabilize the power distribution network and cause damage to equipment connected to the power mains. Safety features may cause substations and generators to be switched off-line, to protect equipment from damage, at the very moment the substations and generators are needed to be on-line to meet load demands. The prevention of such occurrences is one reason electric utility companies will have radio stations broadcast requests, during such outages, for customers to turn off appliances and other loads until after power is restored. If a utility company were able to control and diversify, from a central location, the restoration of power to loads in its service area, it would be able to greatly reduce the threat of, and problems of dealing with, such transients. A utility company, or a governmental entity, might also wish to distribute power selectively to certain types of loads, or withhold power from certain types of loads, during problem situations. For example, during natural disasters and peak load times such as excessively hot summer days, it may be a valid power system management plan to ration power delivered to specific customers, or to specific appliance types, such as water heaters, pool pumps, air conditioners, or low priority (i.e., non-essential) loads in general, in order to prevent generator or distribution system problems. Employing this approach, it may also be possible for the utility company to avoid the expense of building substation or generation capacity solely to be able to withstand such extreme situations.
Other service providers (e.g., water authorities, gas suppliers and cable television companies) have expressed the desire to interact with their customers, also, but so far the systems for doing so are limited and of limited value in light of the cost of installing a pervasive communications network and flexible control systems.
In view of the foregoing, it should be apparent that there exists a need for an automation system for monitoring energy (power) consumed not only by a residential or commercial utility customer as a whole, but also by specific loads operated by the customer. A need further exists for an automation system which is easily operated by a utility customer to permit the customer to control operation of such loads. Desirably, the system will permit the customer to program loads to function or not function in response to energy rate information supplied by the power company and parameters supplied by the customer. In addition, there exists a need for a system that also permits the power company to control selectively such loads.